Effects of plant species, age and part on the disappearance of sevin, nuvacron and malathion residues.

Residues as determined by bioassay using Daphnia or mosquito larvae were in agreement with each other in most cases except sevin residues at 1 h and 8 days after treatment of mallow. The mosquito larvae failed to record nuvacron, sevin and malathion on 45-day-old plants on the 8th, 12th and 24th day, respectively, whereas residues on younger plants continued to affect mosquitoes up to the 12th day and disappeared only on the 24th day. Daphnia continued to show toxicity up to the 24th day on younger and older plants. Insecticide residues of nuvacron, malathion and sevin, found on the leaves 30- and 45-day-old plants of cotton, Jew's mallow and kidney beans after 1 h, 1, 4, 8, 12 and 24 days were estimated biologically by C. pipiens larvae and D. magna. Residues of insecticides disappeared more readily on bean pods than on bean leaves. Residues of sevin, malathion and nuvacron found on the pods 12 days after treatment as indicated by Daphnia were 0.189, 0.055 and 0.059 ppm respectively. They are far less than the corresponding residues on bean leaves. The 1-hour residue was higher on younger bean leaves than on mallow and cotton with very few exceptions (nuvacron, malathion and sevin: 2.125, 11.75 and 95 ppm on cotton leaves; 2.25 and 145 ppm on Jew's mallow and 3.750, 32.500 and 250 ppm on common bean leaves, respectively). These data were obtained with C. pipiens larvae. The picture was completely reversed on 45-day-old plants. 1-h deposits of malathion were higher on mallow than on cotton or beans (nuvacron, malathion and sevin; 2.3, 200 and 140 ppm on cotton leaves, 1.90, 191.15 and 92.86 ppm on mallow leaves, 2.25, 21.5 and 137.5 ppm on common bean leaves, respectively). These data were obtained with C. pipiens larvae. Nuvacron residues on 45-day-old mallow were less on mallow than on cotton or beans. Sevin was higher in 1-h residues on cotton and beans than on mallow. Mallow did not retain insecticides as long as did cotton and beans. The initial concentration of nuvacron was little less than that of sevin and malathion. It was more toxic to mosquito larva (LC50 = 0.0016 ppm) than malathion (LC50 = 0.0034 ppm) and sevin (LC50 = 0.075 ppm). Daphnia was more affected by malathion (LC50 = 0.000098 ppm) than by nuvacron (LC50 = 0.00024 ppm). Nuvacron was nearly equitoxic to sevin (LC50 = 0.00026 ppm) against Daphnia. In spite of this all tested plants, both young or older ones, retained nuvacron in the smallest quantities in proportion to the other insecticides. The 1-h residues were less on older plants (except cotton) for only nuvacron and sevin: 2 and 94.5, 1.9 and 92.8 ppm than on younger ones 2.4 and 137.2, 2.25 and 145 ppm as indicated by Daphnia and mosquito larvae respectively. This emphasizes that the initial concentration is not the limiting factor for the determination of the 1-h residue as the initial concentration was much higher on older than on younger plants.